This invention relates to molded one-piece articles having selected surfaces suitable for adherent metallization or molded metallized articles and processes for forming the articles. More particularly, this invention relates to molded, one-piece blanks for printed circuit boards and molded one-piece articles, such as printed circuit boards; molded, metallized, one-piece articles, such as printed wiring boards; and processes for forming the blanks and metallized articles which include two separate molding steps to form portions of the articles.
U.S. Pat. No. 3,629,185 to F. W. Schneble, Jr. et al describes a process for forming a metallized article, such as a printed circuit board, having an insulating substrate as a base material. The process uses a plastic substrate filled with a powder catalyst which promotes metal deposition in a subsequent electroless metal plating step. The process also includes using a direct or reverse printing technique for preparing specific surface areas of the substrate to form the printed circuit for metallization. When high quantity production is needed, the printing step becomes costly.
U.S. Pat. No. 4,402,135 to Schweingruber et al describes a process for forming printed circuit boards which employs two separate injection molding steps to form a circuit pattern on a support board. In the first step, an electrically insulating plastic material for the substrate is injection molded. In the second step, an electrically conductive plastic material is injection molded. The electrically conductive plastic material is electroplated with metal to form electrically conductive paths. A disadvantage of the method is that an excessive number of gates are required in the second cavity mold to fill several channels on the upper and lower surfaces of the support member to provide a circuit pattern with several electrically conductive paths. Another disadvantage of this method is that the electrically conductive plastic strips may separate or peel off from the support member due to a lack of a rigid connecting structure between the several plastic strips, particularly between the plastic strips on the upper and lower surfaces of the support member. When using a conductive plastic as Schweingruber does, the circuit pattern cannot be molded with a web between conductors in the first molding step, or first shot, because all conductors would short circuit together.